Can an iPhone Replace Your Tools? PM Lab Test

There are iPhone apps for just about everything -- whether it's playing Oregon Trail, or simulating a whoopie cushion. And thanks to the iPhone's built-in accelerometer, the App Store has a whole crop of programs aimed at simulated household tools. We took a skeptical look at four programs that are meant to replace measuring and leveling tools, and gave them to PM's senior home editor and home improvement expert Roy Berendsohn to test. Can an all-in-one tech product replace (some of) your toolbox?

iHandy Carpenter Plumb Bob

Builders, carpenters and masons use plumb bobs all the time to make sure that their constructions are "plumb," or vertically true. The tools typically come as small weights that are suspended from a point using a string known as a plumb line. The iPhone app recreates this experience using the iPhone's accelerometer. As the phone is tilted back and forth or side-to-side, the animated plumb bob swings, and the program tells you how far off plumb you are.

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Roy's Take:

While the program is visually impressive (it looked like a plumb bob that might appear in Myst), it was useless for practical purposes. The problem: It has no inherent ability to find plumb. To work, the user must first calibrate it. This requires positioning it in such a way that you know it's perfectly plumb or level, and then hitting the calibrate button. "But you have no way of knowing whether the surface you are zeroing with is plumb or level in the first place," Roy says. "You could visually tell within a few degrees, but that's not good enough. You would need a level to measure whether it's plumb or level first. If you have those tools, then why the hell would you use this? It's baloney tech."

Worse, the app can't perform the most important purpose of a plumb bob: To draw a straight and plumb line between two points in space (such as one on the ceiling and one on the floor). This is because the iPhone can't be suspended by a string (unless you built some sort of harness for it). As a result, the app can only be used to measure whether an already existing wall is plumb. For this purpose, you'd be better off using a real plumb bob, especially since the back of the iPhone isn't perfectly flat, which will throw off your results.

Bottom Line:

Looks great, but is pretty useless.

iHandy Carpenter Level

You may have seen a virtual spirit level in one of the the iPhone's ads. This is one of several versions available at the iPhone app store.

Roy's Take:

Real levels are designed with flat edges, allowing them to stand on their own. The iPhone's edges are rounded, making it impossible to use this app unless you keep a constant hold on it. But the app's biggest problem is the same as the plumb bob's--it first needs to be calibrated to zero. In order to do this, you must make sure your reference surface is level, necessitating the need for a real level. And if you've got one of those, what are you doing with this app? "I'd much rather use a real level that uses gravity as a built-in calibration tool," Roy says. In practice, iPhone accelerometers aren't even perfectly consistent with each other, so two different iPhones calibrated on the same surface could very well produce slightly different readings.

Bottom Line:

Fun to show off at parties, but nowhere near as useful as a dedicated level.

AccellaRuler

A virtual tape measure. According to the app's official description, it uses "sophisticated processing and your built-in accellerometer to estimate distances ranging from a couple of inches to 15 feet or more. Measurement accuracy is up to 2 percent of the actual distance."

Roy's Take:

The app failed for two reasons. First, it can only be used to measure the distance between two points on a flat surface. To use the app, the user places it on the surface, slides it to the second point, then slides it back to its origin. Real tape measures can span three dimensions. The second, and far more serious, problem is that it's terribly inaccurate. Our results were all over the place, and never remotely resembled reality. A 7-inch distance was pegged to be 22 inches (with a 3-inch margin of error). Roy's take: "This thing is technological overreaching. It'd be like turning the phone into a coffee maker. Why would you do it? A regular tape measure is rapid, accurate and extremely versatile."

Bottom Line:

Stick to a regular tape measure or a laser tape measure. They work in three dimensions, and give you accurate results. This app does neither.

Caliper

A virtual caliper. Use your finger to drag the jaws to the edges of an object and produce precise measurements.

Roy's Take:

Because calipers have jaws that can grip the edges of an object, they are able to provide extremely precise measurements. But the Caliper app only exists on the iPhone screen in two dimensions. As a result, users must eyeball the app's virtual caliper jaws so that they are as close to an object's edge as possible. The results can be close, but they are nowhere near as precise as an actual caliper. "A caliper is a precision instrument, so what good does it do you if it can't provide you precision?" Roy says. The application does work as a ruler, but it's use in that department is limited by the size of the iPhone's screen.

Bottom Line:

The program is passable as a stand-in for a short ruler, but don't expect it to give you caliper-like precision.